The present invention relates to an automatically movable pick-up tone arm for a phonograph turntable. More particularly, it relates to a tone arm for which good tracking conditions are maintained during playing and for which simultaneous detection of the rotational speed of the player turntable and angular position of the tone arm is made.
In a prior art player capable of automatically detecting the angular position of the tone arm as in an automatic record changer, attachments such as a position sensor and a drive magnet have been provided on a rotary shaft of the tone arm to sense the angle of horizontal rotation thereof. However, it is undesirable that such attachements be used because they add weight to and hence increase the inertia of the tone arm. Also, it is necessary to provide an automatic record changer tone arm with a resonance point in a predetermined frequency range taking into account the effects of the elements attached to the tone arm. Contact-type position sensors such as a slide resistor have previously been used to perform the position detecting function. However, the influence of the frictional loss inherent in such a device upon the reproduction sensitivity is not negligible. Therefore, such a sensor has not been found suitable in actual use.
In view of the above-noted defects, an object of the present invention is to provide a highly sensitive tone arm for turntable, specifically an automatic record changer type turntable, which is capable of automatic movement and of accurately detecting the angular position of the tone arm.